This invention relates to a fuel delivery system for a diesel engine. More specifically, the invention relates to a fuel system for premetering specific quantities of fuel to a plurality of fuel injectors prior to injection into the engine.
The fuel system disclosed is related to the fuel system disclosed by Walter et al. in the co-pending patent application entitled "A Dual Solenoid Distributor Pump Fuel System". Walter et al. discloses a fuel system for a diesel engine which includes a distributor pump having two solenoids and a pressure activated diesel fuel injector of the type having a metering chamber and intensifier piston located therein. Diesel fuel is communicated to each of the fuel injectors from the distributor pump through individual bi-directional fuel lines. Each fuel injector is also adapted to communicate with a source of pressurized fuel such that this fuel is selectively permitted to flow into the respective metering chambers in correspondence with the selective activation of one of the two solenoid valves. One of the solenoid valves sequentially controls the metering function for all of the injectors while the other solenoid valve sequentially controls the injection timing function, that is a means for pressurizing the fuel within each metering chamber such that this metered quantity of fuel is injected into the engine in correspondence with the combustion process therein. During the period of time that a particular injector is not within its metering event or injection event, the system disclosed by Walter et al maintains the pressure upstream of the intensifier piston as well as the pressure within the metering cavity at approximately the same pressures. During this idle period of time the intensifier piston of Walter et al is subject to unpredictable movement of drift within its injector housing. This drift of the intensifier piston causes errors in metering a quantity of fuel into the combustion chambers of the engine during subsequent metering and injection events.
Fuel delivery systems for diesel engines can be classified into three broad categories. The first category utilizes distributor pumps having a separate fuel supply line for each injector. The second category of fuel delivery system utilizes a constant pressure source in conjunction with a common rail or manifold which communicates the supply pressure to a plurality of diesel fuel injectors. In this second type of the fuel supply system, the injectors are usually of the type having a pressure intensifier. The third category utilizes what is known as a unit injector which incorporates within the injector a pumping element and the control valve.
The first category of systems does not provide sufficient injection timing control as a function of both engine speed and load. If engine timing is mechanically or hydraulically controlled, this type of system is often inflexible and does not display cycle-to-cycle or cylinder-to-cylinder adaptability for controlling the quantity of fuel injected and its related timing. In addition, high injection pressures such as pressures in the vicinity of 10,000 to 14,000 psi are limited mainly by the strength of the long lines between the pump mechanisms and the injectors. In addition, these types of fuel delivery systems falling within the first category display line cavitation and secondary injections and exhibit a relatively slow termination of injection of fuel into the respective cylinders. Secondary injection and slow termination are primarily a result of poor control of the line dynamics.
The second type of system is amenable to electrically controlling both the injected quantity of fuel and the timing of injection. In addition, the constant pressure--common rail system is capable of delivering relatively high injection pressures. However, this type of system is often extremely expensive and is of a relatively bulky size. The expense and size of the system may be attributable to the fact that the constant pressure source utilizes a pressure regulating device in addition to a number of fuel accumulators, as well as using a 3-way valve which is often required to operate against the high pressure supply. A disadvantage of these systems is high leakage caused by the constant high pressure which is transmitted to each of the fuel injectors.
The unit injector fuel systems provide all of the fuel controls in a single package. However, a significant disadvantage of the unit injector is that the diesel engine must be modified or supplied with separate crankshaft, rocker arms and followers to drive the pumping element of the unit injector. This forecloses the use of the unit injector on standard diesel engines absent a significant redesign or modification of the engine. In addition, since each unit injector must be provided with a control valve the packaging or placement of the injector into the engine or cylinder head is more difficult when compared to the placement and packaging of smaller pressure activated injector valves as utilized by the present invention.
To meet future diesel fuel injection system operating requirements as to fuel economy and emissions control requires high performance. These performance requirements include: (a) high injection pressure of 15,000 psi or more; (b) that the injection system be capable of independent timing and metering control as a function of engine speed and load; (c) that the fuel system be able of controlling its cooperating fuel injector to display injection rate control and display an abrupt termination of fuel injection; (d) that the fuel injection system offer cycle-to-cycle and cylinder-to-cylinder adaptive control; (e) that the fuel injection system can be adapted to standard diesel engines requiring minimum engine change; (f) that the fuel injection system be of low cost and (g) that the fuel injection system display low power input, minimum power drain and low heat buildup.
The above requirements are met by the present invention which broadly includes a dual solenoid distributor pump that is connected individually to a plurality of diesel fuel injectors by bi-directional fuel flow lines. The timing of injection and the quantity of metered fuel delivered to each fuel injector is controlled both on a cycle-to-cycle and cylinder-to-cylinder basis using microprocessor technology by adjusting the electrical signals to two solenoids located within the dual solenoid distributor pump. The drift of the intensifier piston is controlled by incorporating within a distribution valve (of the pump) a distribution slot which is connected to a determinable pressure such that the pressure force so created to communicated in advance of each metering event to the intensifier piston of a particular injector to force that piston to remain at the bottom of its stroke.
An advantage of the present invention is that it may be configured to be packaged and adapted to all sizes of diesel engines with virtually no engine modification. The system utilizes a relatively inexpensive pump in combination with an injector which has a metering chamber. The fuel injection system provides the following advantages: (1) fuel metering is performed at the injector; (2) the injector is provided with a secondary dump port to abruptly end fuel injection; and (3) by utilizing an injector having an intensifier piston therein high pressure lines connected to the pump and injector are eliminated, each injector requires only a single bi-directional injection line and a single low pressure line for fuel metering.
The injector includes an intensifying piston which receives a pressure pulse as a result of the controlled excitation of the timing solenoid valve. The combined features of the distributor pump and injector result in the delivery of fluid at high injection pressures (10,000 to 25,000 psi).
The injector is also provided with a primary dump port and a laminer flow restrictor which functions to depressurize the injection line linking the distributor pump to the intensifier piston, thus preventing line cavitation and secondary fuel injection. This results from incorporating within the distributor pump a positive displacement pump. By utilizing only two valves to control both engine timing and fuel metering, the number of control and timing valves which are found in the prior art are minimized. In addition, by incorporating the control and timing features into the dual solenoid distributor pump permits the relocation of this timing and metering controller away from the limited space near the engine or cylinder head area.
According to the specific embodiments illustrated in the drawings of this application and discussed in detail below, the present invention comprises:
A fuel injection system for a diesel engine having injection and metering modes of operation for delivering fuel from a fuel reservoir to the cylinders of an engine comprising: a plurality of fuel injectors wherein each of the fuel injectors comprise: a housing having a first port adapted to receive fuel at a first determinable pressure level, a second port adapted to receive fuel at a second determinable pressure level and a nozzle, and further having metering chamber means connected to the second port, for storing a premetered quantity of fuel, during the metering mode of operation, prior to the injection of the premetered quantity of fuel into the engine during the injection mode of operation. Each injector further includes piston means reponsive to the differential fuel pressure applied thereacross having a first pressure receiving surface in fluid communication with the first port and a second pressure receiving surface in fluid communication with the second port for reciprocatively moving within the housing for selectively compressing and for causing premetered quantity of fuel to exit the metering chamber means and to be injected into the engine, through the nozzle, during the injection mode and for selectively permitting fuel to reenter the metering chamber means during a subsequent metering mode.
The system further includes manifold means for connecting in fluid communication each of second ports of each fuel injector and pressure regulating means connected between the manifold means and the fuel reservoir for regulating and for supplying fuel at the second determinable pressure to the second inlet port of each of the injectors and for returning to the reservoir excess fuel received from the injectors and distributor pump means connected to the first port of each fuel injector and to the fuel reservoir for sequentially pressurizing the first port of a particular fuel injector at a pressure greater than the pressure established by the pressure regulating means thereby causing the piston to stabilize at the bottom of its stroke and for sequentially thereafter lowering the first pressure level to a pressure lower than that of the pressure established by the pressure regulating means thereby causing the piston to move causing the premetered quantity of fuel to enter the metering chamber of a particular one of the injectors through the second port and for sequentially thereafter increasing the first pressure level thereby causing the piston to pressurize the fuel within the metering chamber to initiate fuel injection into the engine through the nozzle.